In an inertial guidance system the inertial sensors perceive vehicle acceleration which is integrated to determine the vehicle's velocity and position. The major difference of a strapdown system as compared to the gimbal-platform approach is the mechanization used to determine direction of the sensed acceleration. In the gimbaled platform system, the sensors are mounted on a platform whose orientation is maintained by gyroscopic control and is read from gimbal pickoffs. The strapdown accelerometers are fixed to the vehicle and their orientation computed. Information for this computation is obtained from outputs of gyros mounted directly on the body of the vehicle. The gimbal function is performed by the computer.